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Old May 08, 2012, 05:11 PM
jcdfrd is offline
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Originally Posted by corsair nut View Post
maybe it fluttered causing them to rip out. sorry to see that.

how many watts was your setup alan?
cn
thats what I was thinking as well which is why I asked him to post pics but it looks like he maintained mechanical advantage on his linkage setup and looks to be not enough ca on the hinges as James pointed out
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Old May 08, 2012, 05:12 PM
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"Take Off" eh!
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Ive been using simlar hinges in my 25lbs Sprint jet for 3 years now with no issues and close to 200 flights.

just saying..
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Old May 08, 2012, 05:13 PM
db_sonic is offline
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Sorry for the loss. But good rule to always pin the hinges.
Old May 08, 2012, 05:26 PM
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Originally Posted by vettster View Post
Ive been using simlar hinges in my 25lbs Sprint jet for 3 years now with no issues and close to 200 flights.

just saying..
i no i have them in my elan with no problems but i will show u the hinges it has pulled the covering off them so they are clear mylar and its left the white part in the wood
Old May 08, 2012, 05:36 PM
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first and last flight Het super sniper xl (2 min 29 sec)


I have been building planes for a long time now and i asure u there was enough zap ca on them hinges looks like the end 2 hinges gave up first and then riped the other ones out. will get another one for sure they fly loads better than my habu if u go to my youtube page Alanjets i build quite a few and no what im doing
Old May 08, 2012, 05:38 PM
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well we know it was flutter because alan said it fluttered so next is to figure out why it fluttered
Alan can you measure these two points 1)center of servo horn screw out to the clevis hole you used 2) hinge centerline to control horn clevis hole you used these two measurements should be equal or longer length on the elevator control side to eliminate a linkage problem. if its shorter on the elevator side then this was the problem, flutter caused by lack of mechanical advantage in linkage system
Old May 08, 2012, 05:51 PM
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well after watching the video if the control linkages are proper then the next thing I would say is excessive vibration from the fan system caused resonance frequency's to blow up the tail.
alan if I recall correctly doesn't this have the cs 12blade fan in it?....how was the balance? it doesn't sound too good but video's can distort things a bit
Old May 08, 2012, 05:58 PM
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Hey Ya'll!! Watch THIS!!
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Sounds like the fan lost balance on second go around. Camera man even says "What's that noise?"
But on take off it was fine. 1:04
Are we sure the Ele linkage broke AFTER the crash??


And I am just awfully sorry for your loss. That is horrible. So sorry man!
Last edited by Michael Paxton; May 08, 2012 at 06:03 PM.
Old May 08, 2012, 06:07 PM
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Man that sucks, sorry man! I had my Sniper 90 crash first flight when the elevator horn ripped out of the soft balsa. I feel your pain. I have never heard of fan vibration causing a crash before as was suggested in previous posts. Anything can happen I guess. Were all the linkages still attached to the control horns after the crash? Possible any servos came loose....were they glued in or bolted in?
Old May 08, 2012, 06:13 PM
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I just saw the pic of the elevator and thought the same thing. the hinges did not break and did not easily come out based on the fact they ripped the stab apart as they came out. I agree, it appears there is just not enough surface area for the hinges to be glued to.

QUOTE=vettster;21556358]alan...sorry about your loss.. Though it appears as though the problem is not the hinges as they are all in one peice, but more so the surface area holding the hinges since you can clearly see that the area is broken and lifted. Perhaps Flutter?[/QUOTE]
Old May 08, 2012, 06:26 PM
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Quote:
Originally Posted by Tumbler View Post
I just saw the pic of the elevator and thought the same thing. the hinges did not break and did not easily come out based on the fact they ripped the stab apart as they came out. I agree, it appears there is just not enough surface area for the hinges to be glued to.

QUOTE=vettster;21556358]alan...sorry about your loss.. Though it appears as though the problem is not the hinges as they are all in one peice, but more so the surface area holding the hinges since you can clearly see that the area is broken and lifted. Perhaps Flutter?
[/QUOTE]

+1, the hinge surface area near the left knee seems to be 3-4mm thick...maybe not enough to hold the elevator at high speeds
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Old May 08, 2012, 06:30 PM
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Originally Posted by Tumbler View Post
Man that sucks, sorry man! I had my Sniper 90 crash first flight when the elevator horn ripped out of the soft balsa. I feel your pain. I have never heard of fan vibration causing a crash before as was suggested in previous posts. Anything can happen I guess. Were all the linkages still attached to the control horns after the crash? Possible any servos came loose....were they glued in or bolted in?
here's decent decsription of what can happen from resonance frequency vibration, this description relates to full scale aircraft but the same conditions apply to our models

Flutter Excitation

One of the most dangerous events that can occur in flight is a phenomena called "flutter". Flutter is an aerodynamically induced vibration of a wing, tail, or control surface that can result in total structural failure in a matter of seconds. The prediction of flutter is not a precise science and requires flight verification that flutter will not occur within the normal flight envelope.


The aerodynamic surfaces of an airplane are constructed so that they can carry the loads that are produced in flight. For example the wing must be capable of supporting the weight of the airplane as well as the additional lift produced during turning flight. The resulting wing structure can be viewed as a blade or spring extending from the fuselage. If we "tap" the spring with a hammer, it will vibrate at a frequency which relates to the stiffness of the spring. A stiff spring will vibrate at a higher frequency than a more limber spring. This frequency is known as the "natural frequency" of the spring.

Flutter will usually occur at or near the natural frequency of the structure, that is, some small aerodynamic force will cause the structure to vibrate at its natural frequency. If this small force persists at the same frequency as the natural frequency of the structure, a condition called "resonance" occurs. Under a resonant condition, the amplitude of the vibration will increase dramatically in a very short time and can cause catastrophic failure in the structure. this would also coincide with the outer hinges failing first as the amplitude is greatest their

The aerodynamic forces which can induce flutter are related to the dynamic pressure, or airspeed, of the airplane. If flutter-inducing forces are present they will increase as the airspeed is increased. Flutter characteristics can be explored by "tapping" the surface at progressively faster airspeeds, then watching how fast the vibrations decay or damp out. The vibrations will take longer to decay as the airspeed approaches a possible resonant condition. In this way potential flutter can be approached safely without actually reaching the resonant condition and experiencing sustained flutter.

The method for "tapping" the surface varies. On some airplanes a sharp control pulse is sufficient to excite the natural frequency of the surface. In most cases a special flutter excitation device is installed. This device will use either an aerodynamic vane or an unbalanced mass which is driven back and forth at the known natural frequency of the surface. The device is abruptly turned off and the natural damping characteristics of the vibrating surface are revealed. The analysis is similar to the frequency and damping analysis discussed under the "control pulse" maneuver, except that the structural (or flutter) frequencies are much higher.
Last edited by jcdfrd; May 08, 2012 at 06:36 PM.
Old May 08, 2012, 06:41 PM
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"Take Off" eh!
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Again..sorry about your loss Alan...But what a Spectacular crash!!! There's nothing left of it
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Old May 08, 2012, 06:47 PM
AIR SALLY is offline
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deltas are cool
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if it were me i would pin the hinges with round tooth picks or some .050 " C/F rod .sorry to see this happen .again this thread may help others not have this proplem.
the shape of the elev. may not be helping either .....the wider tips than the center section could really amplifiy the flutter or twisting of the elev.plus there is more weight at the tips.i cant think of any airplane (full scale) that has elev. shaped like that.i'd be using 4-40 rod for the controls too .esp. since you guys are packing some big power into these birds.
Last edited by AIR SALLY; May 08, 2012 at 06:54 PM.
Old May 08, 2012, 07:19 PM
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I am very familiar with flutter, but just don't see how the fan vibration has anything to do with it. No fan vibration could equal the vibration you see on a gas or glow plane.

Quote:
Originally Posted by jcdfrd View Post
here's decent decsription of what can happen from resonance frequency vibration, this description relates to full scale aircraft but the same conditions apply to our models

Flutter Excitation

One of the most dangerous events that can occur in flight is a phenomena called "flutter". Flutter is an aerodynamically induced vibration of a wing, tail, or control surface that can result in total structural failure in a matter of seconds. The prediction of flutter is not a precise science and requires flight verification that flutter will not occur within the normal flight envelope.


The aerodynamic surfaces of an airplane are constructed so that they can carry the loads that are produced in flight. For example the wing must be capable of supporting the weight of the airplane as well as the additional lift produced during turning flight. The resulting wing structure can be viewed as a blade or spring extending from the fuselage. If we "tap" the spring with a hammer, it will vibrate at a frequency which relates to the stiffness of the spring. A stiff spring will vibrate at a higher frequency than a more limber spring. This frequency is known as the "natural frequency" of the spring.

Flutter will usually occur at or near the natural frequency of the structure, that is, some small aerodynamic force will cause the structure to vibrate at its natural frequency. If this small force persists at the same frequency as the natural frequency of the structure, a condition called "resonance" occurs. Under a resonant condition, the amplitude of the vibration will increase dramatically in a very short time and can cause catastrophic failure in the structure. this would also coincide with the outer hinges failing first as the amplitude is greatest their

The aerodynamic forces which can induce flutter are related to the dynamic pressure, or airspeed, of the airplane. If flutter-inducing forces are present they will increase as the airspeed is increased. Flutter characteristics can be explored by "tapping" the surface at progressively faster airspeeds, then watching how fast the vibrations decay or damp out. The vibrations will take longer to decay as the airspeed approaches a possible resonant condition. In this way potential flutter can be approached safely without actually reaching the resonant condition and experiencing sustained flutter.

The method for "tapping" the surface varies. On some airplanes a sharp control pulse is sufficient to excite the natural frequency of the surface. In most cases a special flutter excitation device is installed. This device will use either an aerodynamic vane or an unbalanced mass which is driven back and forth at the known natural frequency of the surface. The device is abruptly turned off and the natural damping characteristics of the vibrating surface are revealed. The analysis is similar to the frequency and damping analysis discussed under the "control pulse" maneuver, except that the structural (or flutter) frequencies are much higher.


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